I. Field of the Invention
The present invention pertains to processes for the manufacture of dihydric alcohols. More particularly, the present invention pertains to the production of butanediol. Even more particularly, the present invention pertains to a method for arresting silicate fouling during the production of butanediol.
II. Prior Art
Generally, the production of butanediol and similar dihydric alcohols contemplates the condensation reaction between an aldehyde or ketone with acetylene followed by the hydrogenation thereof, in the presence of a hydrogenation catalyst.
Typically, this catalytic reaction employs a catalyst which is supported on a silica base. Hence, the resulting aqueous solutions of crude butanediol contain some silicates which precipitate as the water is removed during the distillation process. The precipitation of the silicates occur, substantially, in the dewatering section of the distillation train or column. The silicates are deleterious in that they coat the reboiler tubes to such an extent that the heat transfer process is rendered impossible. The first distillation tower and its associated reboilers are those which are predominantly effected by the silicate precipitation.
The prior art has proposed some solutions to these problems. In steam generation plants silicate fouling is controlled by a lime/soda treatment and ion exchange resin treatment. Steam generation plants also employ phosphates to control silicate fouling. However, chemical plants have not adopted these known methods because of their cost, since uninterrupted service is not essential in chemical plants as it is in power plants. Thus, the chemical plants employ different methods. For example, silicates are cleaned out during shutdown periods, such as those forced by the silicate fouling itself and/or scheduled shutdowns. Other methods of overcoming fouling include the partial dismantling of the distillation train with the mechanical cleaning thereof or the utilization of a caustic boil out. The caustic boil out method typically uses a 5% to 10%, by weight, aqueous caustic medium with a minimum contact time of several hours at temperatures greater than 90.degree. C. After the boil out is completed, the distillation towers and reboilers are rinsed to remove excess caustic. It is to be appreciated that this boil out method is not completely efficacious by virtue of the amount of aqueous caustic utilized; the contact times, as well as, the heat generation required for the temperatures. Thus, it is to be appreciated that a major advance in the art could be provided by a simplified method for reducing presilicate precipitation. It is to this end to which the present invention is directed.